Photoflash lamp



W. F. ALBRECHT PHOTOFLASH LAMP Filed Feb. 15, 1957 Jan. 13, 1959 lnvenliow". Warren E. Atbvech t, by ya: A,

IT" His A t vneg.

United States PatentOv PHOTOFLASH LAMP Warren F. Albrecht, Euclid, Ohio,assignor to General. I

Electric Company, a corporation of New York My invention relates tophotographic flash lamps of the type comprising a sealed bulb orenvelope containing a combustion-supporting atmosphere and a charge ofcombustible material which is ignited by an ignition means comprising afulminating primer.

In the presently available commercial flash lamps the ignition meansincludes a fine tungsten filament which is heated to incandescence,usually by a dry cell battery, to ignite the primer which in turnignites the combustible material, the said combustible material usuallyconsisting of a shredded foil of aluminum. While lamps of that type givegood results under proper conditions, yet there exist certaindifliculties such as failure of the lamp to fire if the battery shouldbe weakened or run down or if there should be relatively poor contact inthe circuit, as between the lamp base and its socket, for instance.

It is therefore an object of my invention to overcome the aforesaiddiflficulties by providing a flash lamp and ignition system wherein thefilament is dispensed with. It is a further object to provide afilamentless type flash lamp which is completely reliable in operationeven fro-m an electrical power source possessing very little energy Itis a still further and particularly desirable object to provide a flashlamp which can be flashed reliably by the low energy output of apiezoelectric crystal.

Generally speaking, it has been proposed heretofore to provide afilamentless type photoflash lamp. In one such lamp containing a fillingof combustible foil, a pair of electrodes were arranged in fixed spacedrelation and a fulminating substance was disposed in the gaptherebetween to be ignited by an arc discharge formed between theelectrodes by application of a high voltage current from a transformer.It has also been proposed to provide a flash lamp with a singleelectrode coated with a dielectric and with a primer composition andflashed by a potential of some 10,000 to 20,000 volts to produce a sparkdischarge to ignite the primer and the combustible foil.

Suchprior art lamps require the application of a substantial amount ofelectrical energy for reliable flashing of the lamp, and it is a furtherobject of my invention to provide an improved flash lamp constructionwhich is reliable in operation from a source of substantially lowerelectrical energy level and which does not require a precise fixedelectrode spacing.- Further features and advantages of my invention,including novel features of construction, will appear from the followingdescription of species thereof.

In accordance with one aspect of my invention, I provide a flash lampcomprising a bulb or envelope containing a combustion-supportingatmosphere and a combusin tible metallic material such as shredded foil,and a pair of internal electrodes at least one of which is provided witha primer composition and wherein the combustible material is arranged toprovide a conducting path between the electrodes whereby a power surgewill form small arcs between an electrode and the combustible materialthrough the primer to thus ignite the primer and,

Patented Jan. 13, 1959 through it, the combustible materiaL. The currentflows in a path from one electrode, in an are through its primer coatingto the combustible material and, by conduction through the foil, to theother electrode or, in case the second electrode is also provided with aprimer coating, then to the said primer coating and in an are throughsaid coating to the second electrode, thus completing the circuit.

For a further understanding of the invention, reference may be had tothe following detailed description and to the drawing wherein:

Fig. 1 is a side view, in section, of a flash lamp of uniquedouble-ended construction comprising my inven tion and an electricaloperating circuit therefor;

Fig. 2 is a fragmentary section of a'slightly modified construction; anda 1 Fig. 3 is an elevation of a single-ended type of lamp embodying theinvention. 7

Referring to Fig. 1, the lamp shown therein is of a double-endedconstruction which is made practicable for manufacture on a commercialbasis by the absence of a filament. The lamp comprises aradiation-transmitting bulb 1 preferably of glass and of tubular form.The ends 1 of the bulb are provided with'r educed neck portions 2 towhich are hermetically sealed, preferably by direct fused metal-to-glassseals, metal terminals or contact members 3, here illustrated asslightly dished or concave discs of a metal or alloy capable of sealingto glass, for instance a chrome iron alloy where the bulb 1 is of theusual high expansion glass employed in the'lamp art. Thereis attached toeach of the terminals 3, for example by welding or brazing,-a' wireelectrode 4 which extends into the interior of the bulb and may be madeof any suitable metal such as iron, copper, aluminum, nickel, etc.

One of the electrodes 4 is coated with a porous primer 5 which may be ofthe same composition as that employed generally in the conventionalfilament type flash lamps. Such primers generally comprise a porous mixture of a readily ignitable metallic powder such as zirconium or amixture of zirconium with magnesium, and an oxidizing agent such aspotassium perchlorate, bonded together by a suitable binder such asnitrocellulose. By way of example, a suitable primer composition mayconsist of, by weight, 90% zirconium and 10% potassium perchlorateformed as a suspension in a solution of nitrocellulose in amyl acetateand having a: viscosity about 24 centipoises x grams per cubic cm; In atypical example,

a half inch long electrode carried a total weight of about .00437 gramof the primer.

The bulb 1 contains a filling of a loose mass of combustible material 6,preferably in the form of shredded aluminum foil such as that employedin conventional lamps. The bulb also contains an atmosphere ofcombustion-supporting gas, preferably oxygen at a suitable pressurewhich may be below or above atmospheric. In smaller bulb sizes theoxygen pressure may be some 1200 millimeters.

The lamp shown in Fig. 2 is essentially like that shown in Pig. 1 butwith a modified form of terminal 3 which is cup shaped and has its edgeor rim embedded in the thickness of the neck portion 2- of the bulb 1.

The lamp shown in Fig. 3 is -of a single-ended type comprising a glassbulb 7 of conventional butt seal construction wherein a pair of lead-inwires or electrodes 8 extend into the bulb through the walls'thereof'and are held in spaced relationship by 'a glass bea'd9 fused thereto.The portion of each electrode 8 above the head 9 is coated with a primer10 which may be of the composition referred to above in connection withFig. '1.

In order to prevent short-circuiting of the electrodes 8 by the metallicfoil 11, the portions of the electrodes within the bulb and below thehead 9 are provided with an electrically insulating or dielectriccoating indicated at 12. Conveniently, the dielectric coating 12 may beof a borate composition which is conventionally applied to the leads orelectrodes 8 to assist in forming a good fused'sea'l with the glassbulb 1. The electrodes may be composed of conventional dumet wire whichis a copper-sheathed nickel-iron core wire. The borate coating isremovedfrom'the portions of the'electrodesgabove the bead 9, or at least fromthe extremities thereof, before application of the primer 10 thereto.The bulb 7 is filled with a combustion-supporting gas and may beprovided with a base.13 having a .shell contact 14 and amend contact lSto which are connected the respective lead wires or electrodes 8.

It is an essential feature of my invention that the combustiblefoilfforms a conducting path between the electrodes from which the foil'is physically separated only by the normally insulating porous primercoating on one or both electrodes. Thus, in Fig. l, the foil 6 is indirect contact with the right-hand electrode 4 and with the primercoating on the left-hand electrode 4. In Fig. 3, the foil 11 is inengagement with the primer coatings on both electrodes 8. i

The lamp is flashed by a power surge from a source 16 of relatively highvoltage (say 200 to 500 volts) and short duration (say'20 to 100microseconds). The voltage appearing across the terminals 3 (Fig. 1)forms small arcs in completing a current path inside the lamp. This pathstarts from one electrode 4 (say the left-hand one, arcing through theprimer coating 5 to the foil 6 and through the foil to the .otherelectrode 4, thus completing the circuit. The small arc or arcs thusformed ignite the primer 5 which ignites the foil 6 to flash thelamp. Inthe lamp of. Fig. 3thepath is from one electrode 8, arcing through theprimer coating 10 thereon to the foil 11 which conducts thecurrent tothe primer coating 10 on the other electrode v8, and arcing through thatprimer to the said other electrode to complete the circuit and flash thelamp.

A significant advantage of this construction is that there need be nodefinite fixed spacing between the .electrodes, thereby eliminating theneed for accuracy and making entirely feasible the mass production ofsuch lamps on a commercial basis. The absence of a filament also makespracticable the production of doubleended lamps of the type shown inFig. 1 which lend themselves particularly well to use in magazine typefeeding or loading equipmentemployed with a camera.

A particularly significant advantage of the lamps disclosed herein isthat they are capable of being flashed reliably when a piezoelectriccrystal isemployed as the energy source as indicated at 16 in Fig. 1.The lamps may be flashed successfully when the power source 16 is abattery-transformer combination or a static electricity charge, butit isespecially advantageous that they can be flashed successfully whenemploying a source of such low energy level (in the order of microwatts)as that supplied by a piezoelectric crystal, thereby completelyeliminating the need for a battery with its attendant inconvenience anddisadvantages. To flash the lamp, the crystal 16 -is given a sharp blowto cause it to emit a momentary voltage of steep wave front. WhileRochelle salt crystals may be employed, I prefer to employ a crystal ofbarium titanate which may yield a voltage of some 200 to 1000 volts fora duration of a few microseconds with a total energy in the order ofmicrowatts. A barium titanate crystal of about inch diameter and flrinchthick yielding a potential of about 450 volts has been employedsatisfactorily for this purpose.

It will be noted that the gap between the electrodes 4 or 8 is much toolarge to sustain a discharge directly therebetween through the gaseousatmosphere in the bulb when employing a piezoelectric crystal as thepower source. Inorder tosustain a discharge directly between theelectrodes from a piezoelectric crystal source, the electrode spacingwould have to be of the order of inch; obviously, it would beinordinately difficult to maintain such spacing on a commercial massproduction basis. Neither is it feasible to flash any of the lampsheretofore proposed and of which the applicant is aware, whether of thetype containing a filament or of the arc type, by employing apiezoelectric crystal as the source of power. In the case of thefilament type lamp, the energy level of the surge from the crystal istoo low to heat the filament to a sufficiently high temperature toignite the primer, and in the case of the arc type lamps the energylevel islikewise too low to form an arc in the constructions heretoforeproposed. It is therefore essential for this purpose to employ theconstruction disclosed herein where the combustible foil is arranged toform a conducting path or bridge between a pair of internal electrodes.

In the lamp shown in Fig. 1, it is preferable to coat the entire lengthof the one electrode 4 with the primer 5. However, if desired, theprimer may be applied on only a portion of the length of the electrode,preferably the innermost end portion remote from the terminal 3, and inthat event the remainder of the electrode must be coated with aninsulator or dielectric to avoid shortcircuiting of the two electrodes 4by the metallic foil 6. Such insulating or dielectric coatings mayconsist of an oxide of the metal of the electrode, for instance a copperoxide coating on a copper electrode, or other suitable dielectriccoatings such as the borate coating 12 in the Fig. 3 lamp or a coatingformed by a smoke deposit from a flame burning a mixture of boric acidand Synasol. Synasol is a water white liquid composed of about 100 partsdenatured ethyl alcohol, 5 parts ethyl acetate and one part aviationgasoline.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A photographic flash lamp comprising a sealed radiation-transmittingbulb, a pair of spaced metallic electrodes extending into said bulb, oneof said electrodes having substantially its full length within the bulbcoated with electrically insulating material, at least a portion of saidinsulating material consisting of a primer, a loose mass of metalliccombustible material substantially filling said bulb and in contact withboth the primer on said one electrode and with the other electrode andforming an electrically conducting path therebetween for formatron of aspark discharge between said one electrode and the combustible materialthrough said primer upon appllcatlon of a high voltage current to saidelectrodes, and a combustion-supporting atmosphere in said bulb.

2. A photographic flash lamp comprising a sealed rad1at1on-trans-mittingbulb, a pair of spaced metallic electrodes extending into said bulb,.one of said electrodes having substantially its full length within thebulb coated with electrically insulating primer, a loose mass ofmetalcombustible material substantially filling said bulb and in contactwith both the primer on said one electrode and wlth the other electrodeand forming an electrically conductlng path therebetween for formationof a spark discharge between said one electrode and the combustiblematerial through said primer upon application of a high voltage currentto said electrodes, and a combustionsupporting atmosphere in said bulb.

3. A photographic flashlarnp comprising a sealed ramatron-transmittingbulb, a pair of spaced metallic electrodes extending into said bulb,both said electrodes havingsubstantially their full lengths within thebulb coated with electrically insulating material, at least a portion ofsaid insulating material consisting of a primer, a loose mass ofmetallic combustible material substantially filling said bulb and incontact with the primer onbothsaid electrodes and forming anelectrically conducting path therebetween for formation of sparkdischarges between said electrodes and the combustible material throughsaid primer upon application of a high voltage current to saidelectrodes, and a combustion-supporting atmosphere in said bulb.

4. A photographic flash lamp comprising a sealed tubularradiation-transmitting bulb, a pair of spaced metallic electrodesextending into said bulb from the opposite ends thereof, one of saidelectrodes having substantially its full length Within the bulb coatedwith electrically insulating material, at least a portion of saidinsulating material consisting of a primer, a loose mass of metalliccombustible material substantially filling said bulb and in contact withboth the primer on said one electrode and with the other electrode andforming an electrically conducting path therebetween for formation of aspark discharge between said one electrode and the combustible materialthrough said primer upon application of a high 5. A photographic flashlamp comprising a sealed tubular glass bulb, a pair of disc-likemetallic terminals fusionsealed directly to the edges of respectiveopenings in the opposite ends of said bulb, a pair of metallicelectrodes secured to respective ones of said terminals and extendinginto the bulb, one of said electrodes having substantially its fulllength within the bulb coated with electrically insulating material, atleast a portion of said insulating material consisting of a primer, aloose mass of metallic combustible material substantially filling saidbulb and in contact with both the primer on said one electrode and withthe other electrode and forming an electrically conducting paththerebetween for formation of a spark discharge between said oneelectrode and the combustible material through said primer uponapplication of a high voltage current to said electrodes, and acombustionsupporting atmosphere in said bulb.

References Cited in the file of this patent UNITED STATES PATENTS

